clk: cs2000: mark resume function as __maybe_unused

When power management is disabled, we get a harmless warning:

drivers/clk/clk-cs2000-cp.c:544:12: error: 'cs2000_resume' defined but not used [-Werror=unused-function]

Marking the function as __maybe_unused lets the compiler silently
drop it instead.

Fixes: eade4ccd

 ("clk: cs2000: set pm_ops in hibernate-compatible way")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>